Ebi's Blog_Lumière Technologie_

Second law of Thermodynamics in life

2012-09-30T10:29:00.001-07:00

Energy in 3 consecutive forms: potential, kinetic, internal (Photo credit: Wikipedia)

A rock has potential energy (PE) localized in it when you lift it up above the ground. The rock is the system; everything else it encounters is the surroundings. Drop the rock and its PE changes to kinetic energy (energy of movement, KE), pushing air aside as it falls (therefore spreading out the rock’s KE a bit) before it hits the ground, dispersing a tiny bit of sound energy (compressed air) and causing a little heating (molecular motion energy) of the ground it hits and in the rock itself. The rock is unchanged (after a minute when it disperses to the air the small amount of heat it got from hitting the ground). But the potential energy that your muscles localized in by lifting it up is now totally spread out and dispersed all over in a little air movement and a little heating of the air and ground.

A Hot Frying Pan

A hot frying pan? The iron atoms in a hot frying pan (system) in a room (surroundings) are vibrating very rapidly, like fast "dancing in place". Therefore, considering both the pan and the room, the motion energy in the hot pan is localized. That motion energy will disperse—if it is not hindered, according to the second law. Whenever the less rapidly moving molecules in the cooler air of the room hit the hot pan, the fast-vibrating iron atoms transfer some of their energy to the air molecules. The pan’s localized energy thus becomes dispersed, spread out more widely to molecules in the room air.

Some Rusting Iron

In a chemical reaction such as iron rusting, i.e., iron plus oxygen to form iron oxide (rust), the reactants of iron and oxygen don't have to be at a high temperature to have energy localized within them. Iron atoms (as -Fe-Fe-Fe-) plus oxygen molecules of the air (O-O) have more energy localized within their bonds than does the product of their reaction, iron rust (iron oxide).

That’s why iron reacts with oxygen—to release energy from their combined total of higher energy bonds and form the lower energy bonds in iron oxide. Then, all that difference in energy becomes dispersed to the surroundings as heat i.e., the reaction is exothermic and makes molecules in the surroundings move faster. But remember how chemical reactions occur! Remember that it requires energy to break bonds and therefore to start any reaction there must be some extra energy, an activation energy supplied somehow to break a bond or many bonds in the reacting substances. Then, if the bonds that are being formed in the product are much stronger than those being broken in the reactants, that difference in energy (which usually causes greater motion energy of all the molecules) can feed back to break more bonds in the reactants.

However, in the case of iron reacting with oxygen at normal room temperature around 298 K, the process is very slow because only a few oxygen atoms are moving exceptionally fast and hit the iron just right so an Fe-Fe bond and an O-O bond are broken and an Fe-O bond can form. There isn't enough heat (motion energy) localized in nearby iron atoms, and there are no other unusually fast-moving oxygen molecules. It's a slow process depending on collision of the small amount of fast moving oxygen atoms in the surroundings to make it happen.

Therefore, even in moist air (that speeds up another process yielding iron oxide), iron doesn't react very rapidly with oxygen but it steadily does so and in time, both the iron atoms and the oxygen molecule spread out to the surroundings the portion of their bond energy that iron oxide doesn't need for its existence at that temperature.

A Leaky Tire

Air in a tire is at a higher pressure than the atmosphere around it, so it shoots out even from a small hole. (Every spontaneous physical or chemical process involves the second law!) Those nitrogen and oxygen molecules in the tire each have motion energy but it is far more localized, compressed in the small volume of the tire, than it would be in the huge volume of the atmosphere. Thus, the second law explains why punctures or blowouts occur: the motion energy of those localized molecules will become dispersed and spread out to the lower-pressure, larger-volume atmosphere if it is no longer hindered by the tire walls from becoming so.

A Melting Ice Cube

An ice cube melts in a big warm room. How can the melting of a little ice cube in a warm room maybe 200,000 times bigger than it is be an example of the second law? How could that possibly be a spreading out of energy? But the second law has to do with energy dispersal and there's a little spreading out in that 200,001st part of that total of system plus surroundings!

Lots of things are happening when molecules of the warm air disperse some of their energy to the molecules that are vibrating (like dancing rapidly in one place) in the ice cube. Right at the surface many hydrogen bonds between the water molecules of the ice are broken by the motion energy of the air molecules being transferred to the those surface molecules. (This doesn't change the amount of motion energy of those molecules and therefore their temperature doesn't change. They increase in potential energy due to the hydrogen-bond breaking.) Now, because the water molecules whose hydrogen bonds to other molecules in the rigid ice structure are broken, they are free to form hydrogen bonds to other water molecules that are liquid—they can exchange partners and move from one to another. The vibrational energy that allowed them to dance in place in the crystal is changed to translational energy in the liquid and the molecules can move just a bit.

Thus, although the true picture is just a bit more complex (i.e., it is the closer energy levels in translation than in solid vibration that make the energy far more dispersed in liquid than solid), we can sense that the movement of molecules in liquid water allows the energy to be more spread out than in crystalline ice, even at melting temperature. It is not a matter of order and "disorder"!

Order to Disorder

The second law tells us about energy dispersal, and entropy is the word for how that energy dispersal is measured—how spread out the energy becomes in a system, how much more dispersed it has become compared to how localized it was. Such energy changes and consequent entropy changes are the focus for understanding how and why spontaneous events occur in nature. Only sometimes do the structures or arrangements of molecules in an object help us to see greater or lesser localization of energy (that used to be called "order to disorder").

Now we can understand what scientists have been talking about the last century and a half when they spoke in apparently mysterious sentences like "The entropy of the universe increases toward a maximum." All they meant was simply that energy, everywhere, spreads out as much as it can (and that spreading out of energy is measured by entropy).

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Ship camouflage

2012-09-21T07:25:00.001-07:00

WWI troopship, SS Empress of Russia, painted in "dazzle" camouflage markings (Photo credit: Wikipedia)

Camouflage

Ship camouflage is a form of military deception in which a ship is painted in one or more colours in order to obscure or confuse an enemy's visual observation.

Several types of marine camouflage have been used or prototyped: blending or crisis, in which a paint scheme attempts to hide a ship from view; deception, in which a ship is made to look smaller or, as with the Q-ships, like merchantmen; and dazzle, a chaotic paint scheme which tries to confuse any estimate of distance, direction, or heading. Counter illumination to hide a darkened ship against the slightly brighter night sky was trialled in Diffused lighting camouflage.

The first recorded instance of ship camouflage was in the years 56–54 BC during the Gallic Wars, carried out by Julius Caesar who sent his speculator navigia (scout ships) to gather intelligence along the coast of Britain, the ships painted entirely in green, their crews dressed in green.

In the Age of Sail, deception was often used by ships, and paint was applied ad hoc by ships' captains for temporary tactical advantage. A ship might be painted to look like another, it might have its cannon ports hidden by painted canvas to look harmless, or it might have additional cannon ports painted on to appear more powerful. As one example among many, for one of his battles during 1778–1782, American privateer Jonathan Haraden hid the guns of his ship the General Pickering, to appear as if it were a slow merchant ship. Haraden allowed his ship to be approached at close range by a much faster British privateer, then he quickly pulled the painted canvas away and delivered a full broadside, capturing the enemy. camouflage paint was applied by both sides during the Union blockade of 1861–1865. Blockade runners aiding the Confederates sometimes painted their ships all in mist-grey, to hide themselves in coastal fog. One Union blockade crew may have painted their rowboat white, and its oars, and wore white clothing for a night reconnaissance patrol up an enemy-held river.

In the 1890s, German and French fighting ships were being painted grey. American interest in ship camouflage was given official funding in 1898 during the Spanish–American War when white, light grey, and medium grey paint schemes were evaluated for their ability to hide a ship as seen against the distant sky on the horizon. Artist Abbott Handerson Thayer investigated countershadingcolor schemes to "paint out" natural shadows. British ships began being painted grey in 1903. In 1913, American camouflage experiments included a submarine painted in a three-colour pattern of broad vertical stripes designed by William Mackay, using white stripes to separate green and blue stripes.

A patrol boat of the Royal Norwegian Navy, in a splinter camouflage pattern.

Camouflaged Brazilian Navy riverboat.

Patrol boat in Indonesia (2006).

HMS Helsingborg, one of the Swedish Navy's Visby-class corvettes employs both visual camouflage and anti-radar stealth.

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Tonnage

2012-09-20T22:56:00.001-07:00

Tonnage mark (Photo credit: Wikipedia)

Tonnage is a measure of the size or cargo carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. It is incorrect to use the term "tonnage" to refer to the loaded or empty weight of the vessel itself.

Weight measurements

Displacement is the actual total weight of the vessel (mostly without pay load). It is often expressed in long tons or in metric tons, and is calculated simply by multiplying the volume of the hull below the waterline (i.e. the volume of water it is displacing) by the specific gravity of the water. (Note that the specific gravity will depend on whether the vessel is in fresh or salt water, or is in the tropics, where water is warmer and hence less dense.) For example, in sea water, first determine the volume of the submerged portion of the hull as follows: Multiply its length by its breadth and the draft, all in feet. Then multiply the product thereby obtained by the block coefficient of the hull to get the hull volume in cubic feet. Then multiply this figure by 64 (the weight of one cubic foot of seawater) to get the weight of the ship in pounds; or divide by 35 to calculate the weight in long tons. Using the SI or metric system : displacement (in tonnes) is volume (in m³) multiplied by the specific gravity of sea water (1.025 nominally).

The word "displacement" arises from the basic physical law, discovered by Archimedes, that the weight of a floating object equates exactly to that of the water which would otherwise occupy the "hole in the water" displaced by the ship.

Lightship or Lightweight measures the actual weight of the ship with no fuel, passengers, cargo, water, etc. on board.

Deadweight tonnage (often abbreviated as DWT for deadweight tonnes) is the displacement at any loaded condition minus the lightship weight. It includes the crew, passengers, cargo, fuel, water, and stores. Like Displacement, it is often expressed in long tons or in metric tons.

Metric Tonnes per Centimetre Immersion (usually abbreviated to TPC or TPCMI ) is the number of Metric Tonnes (1,000KG) that need to be loaded on the ship for the salt water draft to increase by one centimetre.

Imperial Tons per Inch immersion (usually abbreviated to TPI) is the number of Imperial Long Tons (2,240 lbs) that need to be loaded on a vessel for the draft to increase by one inch. Old imperial TPI measurements are still occasionally used within the USA and the Panama canal. As no ship has been measured by a Classification Society since the 1950s using Imperial measures, modern TPI figures are therefore a conversion from the original Metric measurements and should not be relied upon to be accurate.

The TPCMI figure is used to calculate the draft of the vessel with a given DWT of cargo loaded. On a typical Panamax Bulk carrier with a TPCMI of 80, it would mean that the ship will sink (Draft increase) by one centimetre for every 80 tonnes of cargo loaded.

Draft The distance, usually measured in meters, between the lowest point of the keel and the waterline which varies dependant on the load (DWT) the vessel has on board

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Stealth aircraft

2012-09-18T09:04:00.001-07:00

English: F-117A Stealth fighter aircraft from the 37th Tactical Fighter Wing, Tonopah Test Range, Nev., line the runway after arriving for an overnight stay while deploying to Saudi Arabia during Operation Desert Shield. Location: LANGLEY AIR FORCE BASE, VIRGINIA (VA) UNITED STATES OF AMERICA (USA) (Photo credit: Wikipedia)

Stealth aircraft are aircraft that use stealth technology to avoid detection by employing a combination of features to interfere with radar as well as reduce visibility in the infrared, visual, audio, and radio frequency (RF) spectrum. Development of stealth technology likely began in Germany during World War II. Well-known modern examples of stealth aircraft include the United States' F-117 Nighthawk (1981–2008), the B-2 Spirit, the F-22 Raptor,and the F-35 Lightning II.

While no aircraft is totally invisible to radar, stealth aircraft make it difficult for conventional radar to detect or track the aircraft effectively, reducing the odds of a successful attack. Stealth is the combination of passive low observable (LO) features and active emitters such as Low Probability of Intercept Radars, radios and laser designators. These are usually combined with active defences such as chaff, flares, and ECM. It is accomplished by using a complex design philosophy to reduce the ability of an opponent's sensors to detect, track, or attack the stealth aircraft. This philosophy also takes into account the heat, sound, and other emissions of the aircraft as these can also be used to locate it.

Full-size stealth combat aircraft demonstrators have been flown by the United States (in 1977), Russia (in 2010) and China (in 2011), while the US military has already adopted three stealth designs, and is preparing to adopt another.

Most recent fighter designs will at least claim to have some sort of stealth, low observable, reduced RCS or radar jamming capability, but as of yet there has been no actual air to air combat experience against stealth aircraft.

The general design of a stealth aircraft is always aimed at reducing radar and thermal detection. It is the designer's top priority to satisfy the following conditions; some of which are listed below, by using their skills, which ultimately decides the success of the aircraft:-

Reducing thermal emission from thrust
Reducing radar detection by altering some general configuration (like introducing the split rudder)
Reducing radar detection when the aircraft opens its weapons bay
Reducing infra-red and radar detection during adverse weather conditions

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The hot bulb engine

2012-09-17T03:06:00.001-07:00

The hot bulb engine, or hotbulb or heavy oil engine is a type of internal combustion engine. It is an engine in which fuel is ignited by being brought into contact with a red-hot metal surface inside a bulb.

Most hot bulb engines were produced as one-cylinder low-speed two-stroke crankcase scavenging units.

The concept of this engine was established by Herbert Akroyd Stuart at the end of the 19th century. The first prototypes were built in 1886 and production started in 1891 by Richard Hornsby & Sons of Grantham, Lincolnshire, England under the title Hornsby Akroyd Patent Oil Engine under licence.

It was later developed in the USA by the German emigrants Mietz and Weiss by combining it with the two-stroke engine developed by Joseph Day. Similar engines, for agricultural and marine use, were built by Bolinder and Pythagoras engine factory in Sweden. Bolinder is now part of the Volvo group.

A Hornsby-Akroyd hot bulb engine, built to the original horizontal cylinder, four-stroke design. This particular engine has been adapted to run on lamp oil.

Akroyd-Stuart's heavy oil engine (compared to spark-ignition) is distinctly different from Rudolf Diesel's better-known engine where ignition is initiated through the heat of compression. An oil engine will have a compression ratio of about 3:1, where a typical Diesel engine will have a compression ratio ranging between 15:1 and 20:1. Furthermore fuel is injected during the intake stroke and not at the end of the compression stroke as in a Diesel.

Operation and working cycle

The hot-bulb engine shares its basic layout with nearly all other internal combustion engines, in that it has a piston, inside a cylinder, connected to a flywheel via a connecting rod and crankshaft. Akroyd-Stuart's original engine operated on the four-stroke cycle (Induction, Compression, Power, Exhaust) and Hornsby continued to build engines to this design, as did several other British manufacturers such as Blackstone and Crossley. Manufacturers in Europe, Scandinavia and in the USA built engines working on the two-stroke cycle with crankcase scavenging. The latter type formed the majority of hot-bulb engine production. The flow of gases through the engine is controlled by valves in four-stroke engines, and by the piston covering and uncovering ports in the cylinder wall in two-strokes.

The type of blow-lamp used to start the Hot Bulb engine.

Blow-lamp being used to heat the Hot Bulb of a Lanz Bulldog tractor.

In the hot-bulb engine combustion takes place in a separated combustion chamber, the "vaporizer" (also called the "hot bulb"), usually mounted on the cylinder head, into which fuel is sprayed. It is connected to the cylinder by a narrow passage and is heated by the combustion while running; an external flame such as a blow-lamp or slow-burning wick is used for starting (on later models sometimes electric heating or pyrotechnics was used). Another method is the inclusion of a spark plug and vibrator coil ignition. The engine could be started on petrol and switched over to oil after it had warmed to running temperature.

The pre-heating time depends on the engine design, the type of heating used and the ambient temperature, but generally ranges from 2–5 minutes (for most engines in a temperate climate) to as much as half an hour (if operating in extreme cold or the engine is especially large). The engine is then turned over, usually by hand but sometimes by compressed air or an electric motor.

Once the engine is running, the heat of compression and ignition maintains the hot-bulb at the necessary temperature and the blow-lamp or other heat source can be removed. From this point the engine requires no external heat and requires only a supply of air, fuel oil and lubricating oil to run. However, under low power the bulb could cool off too much, and a throttle can cut down the cold fresh air supply. Also, as the engine's load increased, so does the temperature of the bulb, causing the ignition period to advance; to counteract pre-ignition, water is dripped into the air intake.Equally, if the load on the engine is low, combustion temperatures may not be sufficient to maintain the temperature of the hot-bulb. Many hot-bulb engines cannot be run off-load without auxiliary heating for this reason.

The fact that the engine can be left unattended for long periods while running made hot bulb engines a popular choice for applications requiring a steady power output such as farm tractors, generators, pumps and canal boat propulsion.

Advantages

At the time the hot-bulb engine was invented, its great attractions were its economy, simplicity, and ease of operation in comparison to the steam engine, which was then the dominant source of power in industry. Condenser less steam engines achieved an average thermal efficiency (the percent of heat generated that is actually turned into useful work) of around 6%.[citation needed] Hot-bulb engines could easily achieve 12% thermal efficiency.

During the 1910s–1950s, hot-bulb engines were more economical to manufacture with their low pressure crude fuel injection and lower compression ratio than Diesel engines.

The hot-bulb engine is much simpler to construct and operate than the steam engine. Boilers require at least one person to add water and fuel as needed and monitor pressure to prevent overpressure and a resulting explosion. If fitted with automatic lubrication systems and a governor to control engine speed, a hot-bulb engine could be left running unattended for hours at a time.

Another attraction was their safety. A steam engine, with its exposed fire and hot boiler, steam pipes and working cylinder could not be used in flammable conditions such as munitions factories or fuel refineries. Hot-bulb engines also produced cleaner exhaust fumes. A big danger with the steam engine was that if the boiler pressure grew too high and the safety valve failed, a highly dangerous explosion could occur (although this was a relatively rare occurrence by the time the hot-bulb engine was invented). A more common problem was that if the water level in the boiler of a steam engine dropped too low the lead plug in the crown of the furnace would melt, extinguishing the fire. If a hot bulb engine ran out of fuel, it would simply stop and could be immediately restarted with more fuel. The cooling water was usually a closed circuit, so no water loss would occur unless there was a leak. If the cooling water ran low, the engine would seize through overheating – a major problem, but it carried no danger of explosion.

Compared with steam, gasoline (petrol), and Diesel engines, hot-bulb engines are simpler and therefore have fewer potential problems. There is no electrical system as found on a petrol engine, and no external boiler and steam system as on a steam engine.

A big attraction with the hot-bulb engine was its ability to run on a wide range of fuels. Even poor-burning fuels could be used since a combination of vaporiser- and compression-ignition meant that such fuels could be made to combust. The usual fuel used was fuel oil, similar to modern-day diesel, but natural gas, kerosene, paraffin, crude oil, vegetable oil or creosote could also be used. This made the hot-bulb engine very cheap to run, since it could be run on cheaply available fuels. Some operators even ran engines on used engine oil, thus providing almost free power. Recently, this multi-fuel ability has led to an interest in using hot bulb engines in developing nations where they can be run on locally produced biofuel. Due to the lengthy pre-heating time, hot-bulb engines were nearly always guaranteed to start quickly, even in extremely cold conditions. This made them popular choices in cold regions such as Canada and Scandinavia, where steam engines were not viable and early gasoline and Diesel engines could not be relied on to operate.

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The Nine Unknown

2012-09-16T10:19:00.001-07:00

The Nine Unknown is allegedly a secret society founded by the Mauryan Emperor Asoka around 270 BC to preserve and develop knowledge that would be dangerous to humanity if it fell into the wrong hands.

The nine books entrusted to the Nine Unknown contain information on (1) Propaganda and Psychological warfare, (2) Physiology, including secrets concerning the "touch of death", (3) Microbiology, (4) Alchemy, (5) Communication, including communication with extraterrestrials, (6) Gravity, and anti-gravity devices (Vimanas, mythological flying machines of ancient India), (7) Cosmology, including hyperspace and time-travel, (8) Light, and a technology capable of modifying the speed of light and (9) Sociology, including rules predicting the rise and fall of empires

In the Illuminatus Trilogy by Robert Shea and Robert Anton Wilson, the Nine Unknown Men are mentioned in the book Leviathan as being the "most mysterious and oldest of all secret society groups."

From the book "The Anglo-American Establishment" by Carroll Quigley, "there is a power somewhere so organized, so subtle, so watchful, so interlocking, so complete, so pervasive, that they had better not speak above their breath when they speak in condemnation of it...Beneath the broad tides of human history there flow the stealthy undercurrents of the secret societies, which frequently determine in the depth the changes that take place upon the surface...The pulsing, squeezing beat of the living organism called the Elite—those in influential positions who are making unwanted decisions for us—have succeeded in bringing forth a global government or New World Order (NWO)...the Nine Unknown Men were founded in 270 BCE by the Indian Emperor Asoka. Asoka had founded the Nine Unknown Men to stop technology from falling into the wrong hands, and to stop society from being destroyed again just like Atlantis and the Rama Empire.The Nine Unknown Men consist of 9 Ascended Masters (people who are enlightened spiritually, extremely intelligent, and want to assist in humanity’s spiritual growth). Alvar Hanso matched this perfectly. The Nine Unknown Men are also supposed to have 9 books, one book for each member, that has information on 9 different subjects. These 9 books studied:

1. Propaganda and Psychological Warfare 2. Physiology 3. Microbiology (including advanced biotechnology) 4. Alchemy 5. Communication (especially with extra-terrestrial life) 6. Gravitation (including the construction of the Vimana, an interstellar saucer type vehicle, and UFOs) 7. Cosmology 8. Light 9. Sociology (including rules concerning evolution of societies and how to predict downfalls).

The “Nine Unknown Men” was founded to protect and develop knowledge and technology that would be dangerous if it fell into the wrong hands, and have been doing so ever since 270 BCE. The Nine were also charged by Asoka with manipulating the culture of India to present an image of a backwards and mystically-oriented people to the outside world in order to conceal the advanced scientific knowledge that was being accumulated within.

Another motivation for Asoka to create this society was because of the alleged distruction of the Rama Empire (which is similar to Atlantis) by advanced weaponry thousands of years ago.

The Nine Unknown Men still exist today, sporadically but anonymously assisting humanity, such as providing the cure for Cholera. It is said to be a secret society that works quietly for the good of humanity.

Each of the Nine Unknown Men are said to be Ascended Masters. They each have a book to keep. Each book is an accumulation of potentially hazardous information in nine specific fields. The 9 subjects of these books are as follows:

Propaganda and Psychological Warfare Physiology Microbiology (including advanced biotechnology) Alchemy Communication (especially with extra-terrestrial life) Gravitation (including the construction of the Vimana, an interstellar saucer type vehicle) Cosmology Light Society (including rules concerning evolution of societies and how to predict downfalls).

The VIMANA The Vimana is an ancient flying craft said to have been used in ancient India. It is also said to be one of the secrets contained in book 6 (gravitation) held by the Nine Unknown Men. An ancient manuscript describes how to build the Vimana, and it was said to run off of the propulsion of electromagnetism.

After a particularly nasty battle to conquer the Kalinga territory, resulting in the deaths of 100,000 soldiers, countless civilians, and 150,000 deportations, in a moment of personal reflection while viewing the battlefield strewn with corpses, Ashoka came to the conclusion that he was tired of being such an unpleasant jerk, commenting, “What have I done? If this is a victory, what’s a defeat then”? This is considered to be the catalyst for his conversion to Buddhism, and the benevolent reign of a new, less homicidal Ashoka. Ashoka decided that some knowledge was simply too dangerous for humanity in their barbaric state (he is said to have been in possession of information from the mythical Rama Empire, an Indian version of Atlantis), and created the secret society of the Nine Unknown Men dedicated to preserving the secrecy of knowledge that could lead to our destruction. Each of the Nine was tasked with guarding and adding to a particular realm of knowledge: (1) Propaganda and Psychological Warfare (2) Physiology (3) Microbiology (4) Alchemy (5) Communication (6) Gravitation (7) Cosmology (8) Light and (9) Sociology. Various famous personages are said to have been in contact with the Nine (according to Jacques Bergier and Louis Pauwels, authors of the fascinating, if somewhat loopy Morning of the Magicians), including Pope Sylvester II, a French consul at Calcutta named Louis Jacolliot (1837-1890), a Pastuer collaborator named Alexandre Yersin, and a variety of important figures in Indian history. Most secret societies have total world domination as an important career goal. Not so much the Nine Unknown Men. I mean, in theory they could if they wanted, but rather they are reportedly dedicated to preventing us from going extinct, lending a helping hand here and there, and staying anonymous. Nice guys. I wonder who else they’re talking to these days. Albert Einstein once remarked, “The secret to creativity is knowing how to hide your sources.” Suspicious. Very suspicious.

It is questioned whether or not the Nine Unknown Men exist today.

From Wikipedia

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Radar in a fighter plane (Nose tip opened)

2012-09-05T00:03:00.001-07:00

The radar in an operational Flanker

Placement Paper Sample

2012-08-28T00:25:00.001-07:00

Placement Paper Pattern

SECTION-1 Mechanical aptitude

SET 1:

1. Stroboscope is used for measuring? A. rpm of the spur gear. B. temperature calibration. C. velocity of the reciprocating engine. d. All the above. e. None of the above. 2. Pneumatic pressure for industrial application?
3. Lathe bed is made of CI because?
4. Carbon is added to steel-to increase hardness
5. Guide ways are hardened by which hardening method?
6. Carbon is added to engine parts to enhance——– property.
7. A metal has K temp gradient and 2K for another metal. If a hot fluid is passed through a pipe the pipe should be made up of a. K inside, 2K outside. b. 2K inside, K outside. c. Any of the above. d. None of the above.
8. Crowning of pulley is done for?
9. If temp increases viscosity of gas &liquid

10. Shear angle in press tool -to avoid burr, easy shear.
11. Hardening of shear face in press tool is to
12. Blank size is equal to size of punch in presswork.
13. Bending moment diagram for a UDL in cantilever beam. a. Parabola. b. Triangle.c. Rectangle. 14. for uniform strength of beam condition req. a) Depth constant, width increases. b) Depth increases, width decreases. c) Both should be increases. d) All the above. e) None of the above.
15. M33*2 bolt size refers
16. For this bolt and nut arrangement what type is suitable a.M6-6nos b.M8-4nos c.M10-2nos d.M12-1 .
17. Rupture stress is
18. If two springs of stiffness K1&K2is in series the equivalent stiffness is
19. Find out odd a. Oxy-acety b. Plasma arc c. Electron beam d. USM
20.butt welding . 21.Welding employed for plastics
22.core prints
23.if carbon is added to petrol what happen
24.While machining does not require lubricant.
25.Dirty filter is changed in to cleaner filter What will happen to the air fuel ratio –in the case of carburettor.
26.internal keyway is machined by
27.Aircraft blades are produced by a. Casting b. Stretch forming c. Forging d. Bending.
28.when water hammer occurs in the case of welding?why

29.No of cranks used in 6 cylinder engine
30.Which grade of CI has most shock absorbing and damping capacity
31.damper is a vibration (dissipater).
32.Piezometer is used to measure a)static pressure b)total pressure c)discharge]
33.which of the following is not a fusion welding a) spot welding. b) arc welding. c) Electron beam welding 34.besides any thickness 2 metals of different materials can be butt welded by a) by adjusting the initial gap. b) By adjusting the current,voltage. c) By adjusting the time of welding.
35.when pulley dia is doubled ,width is kept constant , tension is kept constant key size should be a) Doubled in length. b) Doubled in depth. c) Both twice.
36.thermoplastics can be molded by a) Vacuum molding b) Compression molding c) Injection molding
37.A ……..WEIGHT AT SLOPE B—— WEIGHT THAT IS HANGING FOR EQUILIBRIUM a) A comes down b) B comes down c) A&B oscillates. d) Remains at same.
38) Which load is safe for beam————— a) Point load. b) UDL locally. c) UDL fully. d) UVL.

39) For diesel engine which ratio is high? a) Compression ratio. b) Expansion ratio.
40) Washers are used for providing(bearing area).
41) Which has no differential(train).
42) Constituents of brass (alloy of copper and zinc).
43) Worm And worm wheels are used for— higher reduction.
44) Why in a condenser the pressure drops below vaccum turbine is tripped off(choice:c)
45) Fits will be based on –clerance between mating surface.
46)path traced by water particle flowing from an opening on the bottom of the container is —— Parabolic.

SET 2:

1) The path of jet discharging from bottom opening in a tank of water (parabola with its vertex at opening)
2)water hammer in pipes occur due to(heavy pressurisation of pipe)
3)specific speed of a pump(delivers unit discharge at unit head)
4)for small discharge at high pressure(reciprocating pump is preferred)
5)ultimate tensile stress of mild steel compared to ultimate compressive stress is(more)
6)rupture stress(load at breaking point/neck area)
7)moment diagram for cantilever beam carrying uniformly distributed load will be(parabolic)
8)moment of inertia of an area is always least with respect to(centroidal axis)
9)crowning on pulleys help(for automatic adjustment of belt position so that belt runs centrally)
10)mitre gears are same as (right angled bevel gears having same no.of teeth)
11)stress concentration is caused due to((d)all of above)
12)function of washer is(provide bearing area)13)M33×2(metric threads of33mm O.D and 2mm pitch)
14)key used between shaft and pulley is made from(cold rolled mild steel bars)
15)hardness of steel depends on(shape7distribution of carbides in iron)
16)carbon steel is(an alloy of iron and carbon with varying quantities of Phosphorous&sulphur)
17)hardening of Machine tool guideways by(flame hardening)
18)carriage and tailstock are placed in(different guideways)
19)In welding,arc is too long due to(formation of globules in irregular pattern becoz of wandering of arc)
20)acetylene is stored in(liquid form)
21)purpose of riser is to(help feed casting until all solidification takes place)
22)core prints are used to(form set to support&hold core in place)
23)unlike materials as well as materials of different thickness can be butt welded by(control of presure&current)
24)galvanising is(process of coating of zn by hot dipping)
25)size of shaper is specified by(length of stroke)
26)hardness of wheel(or)grade of wheel refers to(strength of bond of wheel)
27)for grinding harder materials(softer grade is used)
28)dielectric medium in EDM is(kerosene)
29)electroplating requires(1)ac,2)dc,3)high frequency ac)
30)no cutting fluid is used in machining (C.I)
31)use of gap(snap)gauge
32)9.81 kgf=?newton
33)general gas eqn is(pv=mRT)
34)carnot cycle has max. efficiency for(reversible engine)

35)fuel-air ratio in a petrol engine fitted with suction carburettor,operating with dirty air filter as compared to clean filter will be(higher)
36)In S.I engines ,air fuel ratio for idling speed is(1)lean,2)rich…)
37)use of piezometer
38)specific heat values for solid&liquid(one)
39)most ductile metal is(1)gold 2)steel 30C.I 4)Al)
40)aeroplane wings are made of
41)adv.of projection welding over spot welding
42)electrodes of resistance welding are made of(high strength&high conductivity)
43)AIRCRAFT GASTURBINE is made of(timken,haste&inconelalloys)
44)when a spring is cut into two,stiffness becomes
45)shear angle given in punch during piercing or punching operation is due to
46)worm gears used for(1)low redn speed 2)high rednspeed…)
47)helical gears are used(for noise redn)
48)mirror(image) is due to
49)hardest cutting tool material is(tungsten carbide)
50)fit is reqd due to(clearance between two mating parts)
51)damper is used for
52)Thickness(t=0.5cm)shear dis=7cm & tensiles tress=400kg/sq.cm find force reqd in punch?

SET 3:

1. Why CI is used for most m/c tools (dampening).
2. Which of the following does not require cooling medium (CI).
3. Among the following which is most used for vibration and dampening (GCI).
4. Which gear has no axial thrust (herring borne)?

5. Which has no differential (train).
6. When C is deposited on engine piston, what happens?
7. Constituents of brass (alloy of copper and zinc).
8. In a sheet metal blanking process the dia of the blank is equal to —–(dia of punch).
9. Fits will be based on (clearance bet mating parts).
10. C is added to a material why (to increase hardness).
11. Why in a condenser the pressure drops below vacuum turbine is tripped off (choice c).
12. Washers are used for providing (bearing area).
13. Constant enthalpy process (throttling).
14. Hardness of steel depends on (carbon).
15. If two springs of stiffness k1 and K2 is in series the equivalent stiffness is (k1+k2/k1k2).
16. Which one will have uniform strength (choice a) width same depth varying. b) Depth same width varying. c) Width and depth vary proportionally. D) Any of the above. E) None of the above.
17. In a simple row 6 cylinder radial engine how many cranks will be there (1).
18. In which of the following work done is zero (all the above). 19. How internal keyway is made (broaching).
20. Screw threads are made (rolling).
21. In which instrument more measure is taken (outside micrometer).
22. Most common pressure range used for industrial applications (5 to 10 bar).
23. Worm gears are used for (high reduction ratios).
24. Ni is added to CI to increase …(toughness).

SECTION 2
Mechanical comprehension
Basically 4 types

1) asked to find the gear direction of rotation given the driver rotation
2) Minimum effort to lift the load given different types of mechanisms
3) Speed of the gear rotation
4) Water flowing from a channel All were diagrammatic. 8-10 questions from pulleys, gears, and shafts.
SECTION 3 Non-verbal reasoning
These were for picture puzzles:
This part is the easiest of all. You can easily solve it in less than 30 minutes. Certain sequence of
8 pictures will be given and u will be asked to find the 9th one, u will have 8 choices. You can easily solve the first 20-25 questions and others are little difficult.

GD topics:

1. Should Mangers Be Good Technical Personnel?

2. Indian Technical Professionals Wish To Merely Set Up A Career Abroad.

3. Are Indians Less Quality Conscious?

4. Brain drain.

Shape Memory Alloys

2012-08-27T23:49:00.001-07:00

Metals are characterized by physical qualities as tensile strength, malleability and conductivity. In the case of shape memory alloys, we can add the anthropomorphic qualities of memory and trainability. Shape memory alloys exhibit what is called the shape memory effect. If such alloys are plastically deformed at one temperature, they will completely recover their original shape on being raised to a higher temperature. In recovering their shape the alloys can produce a displacement or a force as a function of temperature. In many alloys combination of both is possible.

We can make metals change shape, change position, pull, compress, expand, bend or turn, with heat as the only activator. Key features of products that possess this shape memory property include: high force during shape change; large movement with small temperature change; a high permanent strength; simple application, because no special tools are required; many possible shapes and configurations; and easy to use - just heat. Because of these properties shape memory alloys are helping to Solve a wide variety of problems. In one well–developed application shape memory alloys provide simple and virtually leak proof couplings for pneumatic or hydraulic lines. The alloys have also been exploited in mechanical and electromechanical control systems to provide, for example, a precise mechanical response to small and repeated temperature changes. Shape memory alloys are also used in a wide range of medical and dental applications (healing broken bones, misaligned teeth.)

2. History

First observations of shape memory behaviour were in 1932 by ¨ Olander in his study of “rubber like effect” in samples of gold–cadmium and in 1938 by Greninger and Mooradian in their study of brass alloys (copper–zinc). Many years later (1951) Chang and Read first reported the term “shape recovery”. They were also working on gold–cadmium alloys. In 1962 William J. Buehler and his co–workers at the Naval Ordnance Laboratory discovered shape memory effect in an alloy of nickel and titanium. He named it NiTiNOL (for nickel–titanium Naval Ordnance Laboratory).

Buehler’s original task was finding a metal with a high melting point and high impact resistant properties for the nose cone of the Navy’s missile SUBROC. From among sixty compounds, Buehler selected twelve candidates to measure their impact resistance by hitting them with hammer. He noted that a nickel–titanium alloy seemed to exhibit the greatest resistance to impact in addition to satisfactory properties of elasticity, malleability and fatigue. One day he took some NiTiNOL bars from melting furnace and laid them out on a table to cool. He intentionally dropped one on the floor out of curiosity. The bar produced a bell–like quality sound. Then he ran to the fountain with cold water and chilled the warm bar. The bar was once again dropped on the floor. On his amazement it exhibited the leaden–like acoustic response. Buehler knew that acoustic damping signalled a change in atomic structure that can be turned off and on by simple heating and cooling near room temperature, but he did not yet know that this rearrangement in the atomic structure would lead to shape memory effect it was in 1960 when Raymond Wiley joined Buehler’s research group. He worked on failure analysis of various metals. He demonstrated to his management the fatigue resistance of a NiTiNOL wire by flexing it. The directors who were present at this meeting passed the strip around the table, repeatedly flexing and unflexing it and were impressed with how well it held up. One of them, David Muzzey, decided to see how it would behave under heat. He was a pipe smoker, so he held the compressed NiTiNOL strip in the flame of his lighter. To the great amazement of all, it has stretched out completely. When Buehler heard about that, he realized that it had to be related to the acoustic behaviour he had noted earlier. After this moment, NiTi alloys increased interest of developing applications based on a shape memory alloys.

3. Definition of a Shape Memory Alloy

Shape memory alloys are a unique class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature. The shape memory alloys have two stable phases - the high–temperature phase, called austenite (named after English metallurgist William Chandler Austen ) and the low–temperature phase, called martensite (named after German metallographer Adolf Martens).

Figure 1: Different phases of a shape memory alloy.

The key characteristic of all shape memory alloys is the occurrence of a martensitic phase transformation which is a phase change between two solid phases and involves rearrangement of atoms within the crystal lattice. The martensitic transformation is associated with an inelastic deformation of the crystal lattice with no diffusive process involved. The phase transformation results from a cooperative and collective motion of atoms on distances smaller than the lattice parameters. Martensite plates can grow at speeds which approach that of sound in the metal (up to 1100m/s). Together with fact, that martensitic transformation can occur at low temperatures where atomic mobility may be very small, results in the absence of diffusion in the martensitic transformation within the time scale of transformation. The absence of diffusion makes the martensitic phase transformation almost instantaneous (a first-order transition). When a shape memory alloy undergoes a martensitic phase transformation, it transforms from its high–symmetry (usually cubic) austenitic phase to a low symmetry martensitic phase (highly twinned monoclinic structure). NiTiNOL’s high temperature phase has B2 crystal structure and its low temperature phase has B19’ crystal structure. If one ignores the difference between Ni and Ti atoms, B2 crystal structure is simply body–centred cubic and B19 has the same symmetry as hexagonal–close packed, except that the two species of atoms break hexagonal symmetry making the structure to tetragonal. B19’ is a small distortion from B19. See Figure 2.

A feature of all martensitic transformations is that there are number of equivalent shear directions through which the martensite can form within a region of parent–phase. This results in the formation of martensite variants within the microstructure of a transformed alloy. In Figure 1 at twinned martensite phase, we can see two crystallographically equivalent martensite variants created by different atomic shears from the parent phase. Two opposite shears maintain the macroscopic shape of the crystal block. Such a microstructure, where the shear of one variant is accommodated or “cancelled” by that of the other is known as a self–accommodated structure. Three–dimensional self–accommodation requires a large number of variants (typically up to 48 in many alloys) upon cooling without of applied load the material transforms from austenite into twinned martensite. With heating twinned martensite, a reverse martensitic transformation takes place and as a result the material transforms to austenite. This process is shown in Figure 3. There are four critical temperatures defined. Martensitic start temperature (M_S) which is the temperature at which the material starts transforming from austenite to martensite. Second is martensitic finish temperature (M_f ), at which the transformation is complete and material becomes fully in the martensitic phase. Similar temperatures are defined for reversible transformation. Austenite start temperature (A_S) is the temperature at which the reverse transformation starts and austenite finish temperature (A_f) at which the reverse transformation is finished and the material is in the austenitic phase.

Figure 3: Temperature–induced phase transformation of a shape memory alloy without mechanical loading

We get hysteresis curve for a thermoelastic martensitic transformation as seen on Figure 4. The overall hysteresis between forward and reverse transformation pathways in shape memory alloys is small, typically between 10 and 50 deg. cel. Thermoelastic martensitic transformations form the basis of shape memory alloys behaviour and can be repeated indefinitely as long as high temperature excursions are avoided.

4. One–way memory effect

4.1 Macroscopic range

If an alloy, which is in a state of self–accommodated martensite, is deformed by applying mechanical load and then unloaded, remains deformed. If the alloy is then reheated to a temperature above the austenite finish temperature, it recovers original macroscopic shape. This is so–called one–way memory effect (see Figure 5). As long as the total strain does not induce permanent plastic flow, deformation may be of any type (e.g. tension, compression, bending or more complex combinations)

Figure 5: One–way shape memory effect.

4.2 Microscopic range

During the one–way memory effect internal structural changes take place. When we apply load to the self–accommodated martensite, this structure becomes deformed through variant rearrangement, resulting in a net macroscopic shape change. When the alloy is unloaded this deformed structure remains, resulting in an apparent permanent strain. If the alloy is now reheated to a temperature above the martensitic transformation range the original parent phase microstructure and macroscopic geometry is restored. This is possible because no matter what the post–deformation distribution of martensite variants, there is only one reversion pathway to parent phase for each variant. If the alloy is cooled again under martensitic finish temperature, a self–accommodated martensite microstructure is formed and the original shape before deformation is retained. Thus one–way shape memory is achieved. The maximum strain recovered through this process depends on the shape memory system. Typically longitudinal strain is in the range of 1 to 7 %, in some cases up to 10 %

Figure 6: Stress-strain behaviour during the one–way memory effect.

4.2.1. Martensite variants growth

In the shape memory alloys the interfaces between martensite variants are mobile and their positions can be influenced by external variables. Probably most important is applied stress. The herringbone structure of martensites essentially consists of twin-related, self-accommodating variants. The shape change among the variants tends to cause them to eliminate each other. As a result, little macroscopic strain is generated (Figure 7b). The positions of the martensite interfaces change under the influence of stress, creating a balance of variants whose shears best accommodate the direction of applied strain. The interfaces between variants move to “grow” the most favourably oriented variants and shrink the least favourably oriented. Some variants become dominant in the configuration (Figure 7c). This process creates a macroscopic strain, which is recoverable as the crystal structure reverts to austenite during reverse transformation.

Figure 7: (a) Parent phase of a crystal. (b) Self–accommodating twin–related variants after cooling and transformation to martensite. (c) Variant A becomes dominant when stress is applied. Upon heating, the material reverts to the beta phase and recovers its original shape

Figure 8: Martensite variants grow at different rates when they are subjected to stress. Here is an example of only two variants. In the absence of stress (a) plates of the two variants develop with equal probability. If the material is subjected to tensile stress (b), plates of variant 1 grow at the expense of those of variant 2. If the material is subjected to compression (c), the preference is reversed: variant 2 grow at the expense of variant 1. If the material is bent (d), the variants grow according to whether the crystals are locally under tension or compression.

Figure 9: (TOP) Microstructure of twinned martensite meeting a homogeneous region of austenite in a Cu-Al-Ni alloy. (Bottom) Scanning electron micrograph of Ti51Ni49 alloy showing an average grain size of approximately 20μm.

5. Two–way memory effect

In one–way memory effect there is only one shape “remembered” by the alloy. That is the parent phase shape (so-called hot shape). Shape memory alloys can be processed to remember both hot and cold shapes. They can be cycled between two different shapes without the need of external stress.

Figure 10: Micro structural changes during thermal memory and superelastic phenomena.

Two–way shape memory changes rely entirely on microstructural changes during martensitic transformation which occur under the influence of internal stress. Self–accommodation of the martensite microstructure is lost in the two–way effect due to the presence of these internal stresses. Predominant variants are formed during transformation (i.e. there is an excess of certain variants within the martensite microstructure compared to self–accommodated structures.). This results in achieving deformed martensite phase directly by cooling parent phase under the influence of internal stress. Internal stress may be introduced in a number of ways. Usually we talk about “training” of shape memory alloy. Internal stress must be stable on thermal cycling through the transformation. Internal stress is usually a result of irreversible defects. After each loading–unloading cycle, a small residual strain remains. Irreversible defects can also be created through the presence of particles. Two of the most common training methods create two–way memory

• Cyclic deformation at a temperature below M_f followed by constrained heating in the cold–shape to a temperature above A_f.

• Cyclic deformation between the hot and cold–shapes at a temperature above A_f.

6. Pseudo elasticity or the super elastic effect

It is also possible to induce a phase transformation by applying a pure mechanical load isothermally at a temperature above austenite finish temperature. The result of this load application is fully detwinned martensite and very large strains are observed. The martensite formed in this way is known as stress–induced martensite and is only stable under the application of stress. On unloading, the reduction in stress and surrounding elastic forces generated during transformation cause the martensite to shrink back to the original parent phase. This effect is known as pseudoelastic or superelastic effect

Figure 11 shows the mechanical behaviour of such superelastic material, and compares it to a conventional metallic alloy. Such superelastic materials can fully recover deformations up to 6-7 % strain, depending on alloy type.

Figure 12: Comparison of the stress–strain curves of conventional and superelastic alloys.

7. Commercial shape memory alloys

Despite of growing list of alloys that display shape memory effect only two alloy systems have achieved any level of commercial exploitation. These are NiTi (nickel–titanium) and copper–based alloys. Properties of both systems are quite different. The NiTi alloys have greater shape memory strain (up to 8 % versus 4–5% for the copper–based alloys), tend to be much more thermally stable, have excellent corrosion resistance and have much higher ductility. On the other hand, the copper– based alloys are much less expensive, exhibit higher actuation temperatures (approximately in the range -200 to +200 deg. cel.) than NiTi alloys and are sometimes the only choice for high temperature applications (i.e. above 100 deg. cel.). Unfortunately, these copper–based alloys tend to suffer from low strength and poor corrosion resistance.

7.1. Nickel–titanium shape memory alloys

Nickel–titanium alloys have far greatest recoverable strains of commercially available shape memory alloys. Fully recoverable strains of 7% are easily achieved with these alloys. The temperature at which the phase change associated with the memory effect takes place can be adjusted from −200 deg. cel. To +100 deg. cel. by altering the propositions of nickel and titanium around the equi–atomic ratio of 50 % nickel and 50 % titanium. Differences of just 0.1 atomic percent can easily change transformation temperatures by 20deg. cel. or more. For this reason production and processing of NiTi alloys must be very strictly controlled. The manufacture of NiTi alloys follows closely the procedures of conventional titanium alloy manufacture. Because titanium easily forms oxides, carbides and nitrides a vacuum melting process is essential. This ensures good homogeneity of the alloy, and enables transformation temperatures to be controlled to within 5 deg. cel.. Because of this careful fabrication and often small production are NiTi alloys rather expensive.

The greatest benefit of NiTi alloys over other commercial shape memory alloys is its excellent corrosion resistance. The passive titanium dioxide (TiO2) surface film results in a corrosion resistance comparable to 316L stainless steel. Formation of this film is exactly the same as for pure titanium. The film is very stable and resistant to many forms of potentially corrosive attack NiTi’s corrosion resistance has lead to studies on bio–compatibility of these alloys and a number of medical applications. Result of studies was that bio-compatibility is excellent. Organs are showing no signs of metallic contamination. It is thought that the titanium–rich oxide surface prevents nickel (potentially harmful) coming in touch with tissue. This has resulted in a great research activity of NiTi alloys in medicine.

Figure 13: The surface of NiTi clamp before implatantion (top) and after 17 months exposure in the human body (bottom). There is no trace of corrosion visible. Porosity can be neglected on this scale (_ 10μm).

7.2. Alloy Types

Since the discovery of Ni-Ti, at least fifteen different binary, ternary and quaternary alloy types have been discovered that exhibit shape changes and unusual elastic properties consequent to deformation. Some of these alloy types and variants are shown in table 1.

Table 1. Shape memory alloy types.

· Titanium-palladium-nickel

· Nickel-titanium-copper

· Gold-cadmium

· Iron-zinc-copper-aluminium

· Titanium-niobium-aluminium

· Uranium-niobium

· Hafnium-titanium-nickel

· Iron-manganese-silicon

· Nickel-titanium

· Nickel-iron-zinc-aluminium

· Copper-aluminium-iron

· Titanium-niobium

· Zirconium-copper-zinc

· Nickel-zirconium-titanium

The original nickel-titanium alloy has some of the most useful characteristics in terms of its active temperature range, cyclic performance, recoverable strain energy and relatively simple thermal processing. Ni-Ti and other alloys have two generic properties thermally induced shape recovery and super- or pseudo-elasticity. The latter means that an SMA in its elastic form can undergo a deformation approximately ten times greater than that of a spring-steel equivalent, and full elastic recovery to the original geometry may be expected. This may be possible through several million cycles. The energy density of the alloy can be used to good effect to make high-force actuators - a modern DC brushless electric motor has a mass of 5-10 times that of a thermally activated Ni-Ti alloy, to do the same work.

The super elastic Ni-Ti alloys are “stressed” by simply working the alloy. These stresses can be removed, just as with many other alloys, by an annealing process. The stressed condition is termed stress-induced martensite, which is the equivalent of being cold/hot worked.

SMAs, particularly nickel-titanium, are commercially available from several sources. However, world production is small compared to other metal commodities (about 200 tonnes were produced 1998) owing to difficulties in the melt/forging production process, and so the cost of the material high US$0.30-US$1.50 (UK£0.20-£1.00) per gram for wire forms 1999 prices). Fortunately, most current applications require only small amount of the material. As world production increases (as it has done quite dramatically in the 1990s) so prices should decrease. Wires, strip, rod, bar and sheet are all readily available and alloy foams, sintering powders and sputtering targets of high purity are also produced.

7.3. PROGRAMMING

The use of the one way shape memory or super elastic property of NiTi for a specific application requires a piece of SMA to be molded into the desired shape. The characteristic heat treatment is then done to set the specimen to its final shape. The heat treatment methods used to set shapes in both the shape memory and the super elastic forms of NiTi are similar. Adequate heat treatment parameters are needed to set the shape and properties of the item

The two way memory training procedure can be made by SME training or SIM training. In SME training the specimen is cooled below M_f and bent the desired shape. It is then heated to a temperature above A_f and allowed freely to take its austenite shape. The procedure is repeated 20 – 30 times which completes the training. The sample now assumes its programmed shape upon cooling under M_f and to another shape when heated above A_f

In SIM (stress induced martensite ) training the specimen is bent just above M_S to produce the preferred variants of SIM and then cooled below M_f temperature. Upon subsequent heating above the A_f temperature the specimen takes its original austenitic shape . This procedure is repeated 20-30 times

8. Applications of shape memory alloys

Shape memory alloys have wide range of use. That is why categories of application have been introduced

8.1. Free recovery

This category of shape memory alloys is deformed while in a martensitic phase. The only function required is that they return to previous (parent) shape upon heating. A prime application is a blood–clot filter. The filters are constructed from NiTi wires and are used in one of the outer hearth chambers to trap blood clots, which potentially could cause serious health problems if travelling around the blood circulation system. The blood–clot filter is introduced in a compact cylindrical form about 2.0-2.5 mm in diameter. The body heat causes transformation to its functional shape. The wire is shaped to anchor itself in a vein and catch passing clots.

Figure 14: The blood–clot filter.

8.2. Constrained recovery

The alloy is prevented from full shape recovery. This means that the alloy generates stress on the constraining element. The most successful example of this type of product are hydraulic–tube couplings. This kind of couplings was on the first place made for F–14 jet fighter. Coupling is machined at normal temperature to have inner diameter 4 % less than the outer diameter of the tubes to be joined. After cooling the coupling under the M_f temperature, the diameters are expanded to have greater diameter than the tubes (see Figure 19 top). When the coupling is warmed to austenite phase, it shrinks in diameter and strongly holds the tube end together (see Figure 19 bottom). The tubes prevent the coupling to recover its original shape. This creates stresses powerful enough to create a joint, which is better than a weld.

Figure 15: Hydraulic–tube couplings. First couplings were made for F–14 jet fighter from Ni–Ti alloy, now are usually made from Cu-Zn-Al alloy.

8.3. Actuation recovery

The alloy is able to recover its shape but operates against applied stress, resulting in work production.

One application of this group is a temperature–actuated switch. The switch can be designed so that it opens or closes above particular temperature (see Figure 20). Those switches are usually applied in instruments for safety purposes. One such example is a fire safety switch, which is designed to shut off the electricity or flammable gas flow when fire occurs .

Figure 16: Temperature–actuated switch. If the switch is designed to close above the A_f temperature (top), a straight rod of alloy in initial shape is cooled to martensite phase (red colour). Then an alloy is reshaped under stress. When the rod is heated above A_f temperature, the martensite disappears and the rod straightens, closing the switch. If the switch is designed to open above A_f temperature, the rod must be bent before cooling (bottom). The rod is then straightened out before it is placed in the switch.

8.4. Superelastic recovery

The only isothermal application of the memory effect, superelastic recovery involves the storage of potential energy through comparatively large but recoverable strains. This is commercially used in orthodontic applications, especially in correcting misaligned teeth. Superelastic NiTi wires are used for making continuous, gentle, corrective force to give large rapid movement of teeth. Based on clinical observations the optimal forces for tooth movement are 0.5−1.25N . The forces at the lower end of the range correspond to the smaller rooted teeth and the forces at the upper end of range are optimal for the larger rooted teeth. Optimal wires are from NiTi alloy with diameter from 0.4 mm to 0.6 mm. Similar shape memory alloy devices are used for healing broken bones. Staples of the shape memory materials are attached to each part of broken bone. These staples apply a constant, well–defined force to pull the two pieces together. This force helps to heal up the two pieces of bone together.

Figure 17: Arch wires for orthodontic correction of misaligned teeth (top) and TiNi shape memory clamps for healing broken bones (middle, bottom).

8.5. Aircraft Maneuverability

Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance.

Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain.
Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.

The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system attached to it at the point of the actuator connection. "Smart" wings, which incorporate shape memory alloys, are typically like the wing this system is much more compact and efficient, in that the shape memory wires only require an electric current for movement.

Figure 18 :Hinge less shape memory alloy Flap

The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current, which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced.

Current examples of applications of shape memory alloys.

 Aids for disabled

 Aircraft flap/slat adjusters

 Anti-scald devices

 Arterial clips

 Automotive thermostats

 Braille print punch

 Cold start vehicle actuators

 Contraceptive devices

 Electrical circuit breakers

 Fibre-optic coupling

 Fire dampers

 Fire sprinklers

 Gas discharge

 Graft stents

 Intraocular lens mount

 Kettle switches

 Keyhole instruments

 Key-hole surgery instruments

 Micro-actuators

 Mobile phone antennas

 Orthodontic arch wires

 Penile implant

 Pipe couplings

 Robot actuators

 Rock splitting

 Root canal drills

Satellite antenna deployment

Scolioses correction

 Solar actuators

 Spectacle frames

 Steam valves

 Stents

 Switch vibration damper

 Thermostats

 Underwired bras

 Vibration dampers

9. Advantages and Disadvantages

Some of the main advantages of shape memory alloys include:

Bio-compatibility

Diverse Fields of Application

Good Mechanical Properties (strong, corrosion resistant)

The use of NiTi as a biomaterial has severable possible advantages. Its shape memory property and super elasticity is unique characteristics and totally new in the medical field. The possibility to make self-locking, self expanding and self- compressing thermally activated implants is fascinating. As far as special properties and good bio compatibility are concerned, it is evident that NiTi has a potential to be a clinical success in several applications in future.

There are still some difficulties with shape memory alloys that must be overcome before they can live up to their full potential. These alloys are still relatively expensive to manufacture and machine compared to other materials such as steel and aluminium. Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.

Archimedes' principle

2012-08-27T23:23:00.002-07:00

Archimedes' principle is a law of physics stating that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid the body displaces. In other words, an immersed object is buoyed up by a force equal to the weight of the fluid it actually displaces.

Archimedes' two-part treatise on hydrostatics, called On Floating Bodies, states that

Any object, wholly or partially immersed in a fluid, is buoyed up by a
force equal to the weight of the fluid displaced by the object.

Suppose a rock's weight is measured as 7 newtons when suspended by a string in a vacuum with gravity acting upon it.Suppose that when the rock is lowered into water, it displaces water of weight 2 newtons. The force it then exerts on the string from which it hangs would be 7 newtons minus the 2 newtons of buoyant force: 7 − 2 = 5 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor. It is generally easier to lift an object up through the water
than it is to pull it out of the water.

BASIN DRY DOCKS

2012-08-27T11:08:00.002-07:00

Basin or graving docks are large, fixed basins built into the ground at water’s edge, separated from the water by a dock gate.
Basin docks are capable of docking all sizes of vessels, with capacities of over 200,000 tons.
Its basic structure consists of a floor, sidewalls, head (front) wall and a dock gate. Alters (steps) may be incorporated into the side walls for structural stability.

2 – FLOATING DRY DOCKS
Floating dry docks are structures with sufficient dimensions, strength, displacement and stability to lift a vessel from the water using buoyancy.
Floating docks range in lift capacities from a few hundred tons to over 100,000 tons. In general the most economical range for floating docks is about 1,000 to 100,000 tons.

3– MARINE RAILWAYS
A marine railway is a mechanical means of hoisting a ship out of the water along an inclined plane.
Lift capacities range from 100 to 6,000 tons.
Theoretically, even larger sizes are possible, but generally the floating dock becomes a more economical alternative

4 – VERTICAL LIFTS
A vertical lift is a mechanical means of hoisting a ship out of the water vertically.
The dock consists of:

Platform
Hoisting mechanism
Hoist support pier

The platform is lowered into the water until sufficient water over the blocks is achieved. The ship is floated over the platform and centered. The platform is raised, grounding the vessel on the blocks.
As the vessel is raised, all motors are synchronized to insure they each haul at the same rate no matter what the load on each of them is. This insures that no unit gets overloaded.

5 – MARINE TRAVEL LIFTS
A marine travel lift is a vertical lift on wheels.
Instead of a structurally rigid platform to support the vessel, nylon straps are usually used.
The slings are lowered into the water until sufficient water over the slings is achieved.
The ship is floated over the slings and centered. The slings are raised to lift the vessel. Once the ship is at yard’s elevation, the travel lift can be moved under its own power to place the ship on fixed blocks in a storage berth.
The most popular type of travel lift is the “Marine travel lift” of Sturgeon Bay, Wisconsin.
Capacities range from 7 to 500 tons

Various dry docks

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Cruise Ship Technology

2012-08-27T07:08:00.002-07:00

Azipod is the registered brand name of the ABB Group for their azimuth thruster. These are marine propulsion units consisting of electrically driven propellers mounted on a steerable pod.

Azipod system used on ships is combination of both propulsion and steering systems. In conventional propulsion system, a large two stroke engine is connected to a shaft, which passes through shaft tunnel and stern tube and connects to the propeller outside the hull in the aft part of the ship. The steering of such system is done with the help of a rudder placed in the aft of the propeller.

Advantages of Azipod System

1) Greater manoeuvrability as the propeller can be turned in all directions. This enables better stop distance during crash manoeuvring than that provided by the conventional system.

2) In case of ships having large breadth, two or more azipods which are independent of each other can be used. This provides subtle manoeuvring.

3) It saves a lot of space in the engine room as there is no engine, propeller, shafting and other arrangements. The saved space can thus be used for storing more cargo.

4) The system can be placed below the ship’s height thus providing more efficiency than the conventional system.

5) Use of side thruster is eliminated as the pods can be used for providing the side thrust.

6) Low noise and vibrations than the conventional system.

7) Low fuel and lube oil consumption.

8) Environment friendly as emissions are extremely low.

Aluminium’s corrosion resistance

2012-08-24T08:21:00.001-07:00

Untreated aluminium has very good corrosion resistance in most environments. This is primarily because aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation.

Aluminium oxide is impermeable and, unlike the oxide layers on many other metals, it adheres strongly to the parent metal. If damaged mechanically, aluminium’s oxide layer repairs itself immediately.

This oxide layer is one of the main reasons for aluminium’s good corrosion properties. The layer is stable in the general pH range 4 – 9.

The most common types of corrosion are:

galvanic corrosion
pitting
crevice corrosion

Stress corrosion, which leads to crack formation, is a more special type of corrosion. It occurs primarily in high-strength alloys (e.g. AlZnMg alloys) where these are subjected to prolonged tensile stress in the presence of a corrosive medium.
This type of corrosion does not normally occur in common AlMgSi alloys.

DRY DOCK TYPES

2012-08-19T09:28:00.001-07:00

There are several basic types of dry docks:

Basin or Graving docks
Floating Dry Docks
Marine Railways
Vertical Lifts
Marine Travel Lifts

Metacentric height

2012-08-19T07:38:00.001-07:00

The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger metacentric height implies greater initial stability against overturning.

Metacentric height also has implication on the natural period of rolling of a hull, with very large metacentric heights being associated with shorter periods of roll which are uncomfortable for passengers. Hence, a sufficiently high but not excessively high metacentric height is considered ideal for passenger ships.

Metacentre is determined by a ratio of the inertia resistance of the boat divided by the volume of the boat. (The inertia resistance is a quantified description of how the waterline width of the boat resists overturning.) Wide and shallow or narrow and deep hulls have high transverse metacentres (relative to the keel), and the opposite have low metacentres; the extreme opposite is shaped like a log or round bottomed boat. Ignoring the ballast, wide and shallow or narrow and deep means the ship is very quick to roll and very hard to overturn and is stiff. And log shaped round bottomed means slow rolls and easy to overturn and tender.

Engineering Facts

2012-08-19T00:11:00.001-07:00

Engineers solve practical problems by applying mathematical and scientific knowledge.
The word engineer comes from a Latin word meaning ‘cleverness’.
As of 2010, the tallest building in the world is the Burj Khalifa in Dubai, UAE. It reaches an incredible 828 metres (2717 feet) in height. Check out more building facts or our list of the tallest buildings in the world.
The building of the Panama Canal, which links the Atlantic and Pacific Oceans, was one of the most difficult engineering projects ever. It is estimated that over 25000 workers lost their lives during the long and dangerous project, with most dying from disease and landslides.
Golf balls have dimples because they help reduce drag, this allows the ball to fly further than a smooth ball would.
Used for water distribution, the Delaware Aqueduct in New York, USA is the longest tunnel in the world (as of 2010). Drilled through solid rock, it reaches a staggering 137 kilometres (85 miles) in length. More tunnel facts.
The Hoover Dam, built along the Colorado River between 1931 and 1936 reaches 726 feet in height (221 metres). More interesting dam facts.
High speed passenger trains in China reach speeds of up to 350 kph (220 mph).
The London Eye in England is the largest Ferris wheel in Europe, standing at a height of 135 metres (442 feet).
The tallest wind turbine in the world has rotor tips that reach over 200 metres (656 feet) above the ground.

Facts

2012-08-19T00:09:00.001-07:00

As a Mechanical Engineer you can work in a an office using tiny measuring instruments to enormous air craft hangers and power plants using giant machines.

There are hundreds of thousands of jobs for Mechanical Engineers all over the world, as a Mechanical Engineer, you will be unscathed by the worsening economy.

As always with an Engineering job, there is the money, an average income for Mechanical Engineers in 2007 was $75,130.

Mechanical Engineers develop and use new materials and technologies. They design using the most advanced computer systems and software.

What are KSAs?

2012-08-19T00:05:00.001-07:00

KSAs -- Knowledge, Skill, Ability
Specific KSAs are needed in performing certain jobs. Individual KSAs are demonstrated through qualifying experience,
education, or training. KSAs are defined as:

          Knowledge - an organized body of information, usually factual or procedural in nature. For example, having know ledge of human resources' rules and regulations could be used as a KSA for a Human Resources Specialist position. To respond to this KSA, you should indicate w hat human resources rules and regulations you are familiar with, discuss how you applied these rules and regulations in the work environment, and describe other significant situations you w ere involved in w here you applied these rules and regulations.
           Skill - the proficient manual, verbal, or mental manipulation of data or things. For example, having skill with operating personal computers could be used as a KSA for an Office Automation position. To respond to this KSA, you should indicate w hat type of personal computers you have operated, discuss the various types of software programs you have used, and describe how these programs w ere used in your work environment.
          Ability - the power or capacity to perform an activity or task. For example, having the ability to use a variety of laboratory instruments could be used towards a Laboratory Technician position. To respond, you should describe the types of laboratory instruments you have used, discuss the types of assignments you completed using the laboratory equipment, and describe the impact using the laboratory equipment had on your work environment.

Importance of KSAs
KSAs are used to distinguish the "qualified candidates" from the "unqualified candidates" for a position.
A vacancy announcement will list the KSAs in terms of "specialized experience" requirements. You w ill be evaluated against each KSA to see if you qualify. You must show either the relevant education requirements or one year of experience that show s the KSA requirements. Some positions might also have KSAs listed as "selective factors" that are unique requirements for that position. If there are selective factors listed on the vacancy announcement, you should address your experience that is relevant for each selective factor requirement. If you do not, you w ill not receive further consideration in the evaluation process. A resume is important to the job application process since it show s your general experience, education, activities, and other accomplishments. The KSAs listed in the job opening are also important because the KSAs provide you with an opportunity to draw attention to and expand on the specific factors the agency is looking for and provides an opportunity for you to spell out why you are the best qualified candidate for the job.
If you choose to rely on your basic application rather than w rite separate responses to the KSAs, you should be sure that your basic application covers all the KSAs. As an applicant, it is your responsibility to show how your education and experience meet the requirements for positions.

Writing Your KSA Responses
To prepare responses to KSAs:

Read the vacancy announcement thoroughly.
Review your resume.
Add information relevant to each KSA.
Link all of these different examples explicitly to the KSAs.
W rite your KSAs in the first person.
Focus on any outcomes to which you directly contributed.
Make sure your answers reflect your level of responsibility.
Target each KSA answer to read between half a page and a page in length.
Review your answers.
Ask a friend who know s you w ell to read over your finished answers.

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BASIN DRY DOCKS

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Aluminium’s corrosion resistance

Untreated aluminium has very good corrosion resistance in most environments. This is primarily because aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation.

Aluminium oxide is impermeable and, unlike the oxide layers on many other metals, it adheres strongly to the parent metal. If damaged mechanically, aluminium’s oxide layer repairs itself immediately.

This oxide layer is one of the main reasons for aluminium’s good corrosion properties. The layer is stable in the general pH range 4 – 9.

DRY DOCK TYPES

Metacentric height

Engineering Facts

Facts

As a Mechanical Engineer you can work in a an office using tiny measuring instruments to enormous air craft hangers and power plants using giant machines.

There are hundreds of thousands of jobs for Mechanical Engineers all over the world, as a Mechanical Engineer, you will be unscathed by the worsening economy.

As always with an Engineering job, there is the money, an average income for Mechanical Engineers in 2007 was $75,130.

Mechanical Engineers develop and use new materials and technologies. They design using the most advanced computer systems and software.

What are KSAs?

Ebi's Blog_Lumière Technologie_